It's 5.30 and A S Byatt was expecting me at five. But she has put the time to good use. She's been catching up on O'Sullivan and Higgins jousting for the Snooker World Championship.

Antonia Byatt is an unlikely snooker fan, but a keen one. She likes the way the light glances off the balls (pink is her favourite) and the fact that someone wins outright and is not simply judged to have won. The Booker prize, which Byatt scooped in 1990 with Possession, is altogether different. Winning is largely down to luck, the jury and whatever else is published that year. When Byatt won, the decision was not unanimous.

Winning changed her image and gave her confidence. Previously, Byatt was considered a welterweight whose novels were crammed with complicated ideas, frequent references to Milton and Wordsworth and mind-stretching words like quiddity and horripilant. Suddenly, Possession became a massive bestseller, here and in America. Publishers from both countries had 'begged' her to make the book more accessible by removing the Victorian poetry, correspondence and pastiche. Byatt, the bluestocking, almost despaired. 'I did think: 'You're just going to have to give up and write women's-novely novels'.'

But Byatt didn't and hasn't. Her new work, Babel Tower, is part three in a tetralogy which includes The Virgin In the Garden and Still Life. With its examination of language, pornography, censorship, group life and DNA, it is, if anything, more ideas-led than its predecessors.

Byatt doesn't like interviews. She never quite relaxes, although we dip into subjects as varied as her grandchildren and how 'one should feed small children delightful words' to her unexpected admiration for Georgette Heyer's 'deeply moving' romantic novels.

She had a Quaker upbringing. 'I'm not very interested in myself. I do have a deep moral belief that you should always look out at other things and not be self-centred.'

Byatt is sufficiently worldly, however, to accept that others find her fascinating - partly because of her younger sister, Margaret Drabble. Good friends now, they weren't always and their rivalry fed their respective novels.

'You've very nicely not talked about Maggie,' Byatt tells me. 'If I hadn't been a driven writer, I would have quietly given up when she first published a novel. It would have been much the easiest thing to do.' She looks away, signalling that she'd rather not say more. 'It doesn't matter now, but it did once, when one was first writing and it was all anyone wanted to know about.'

The sisters come from a highbrow Yorkshire family. Their father, a judge, studied at Cambridge; so did their mother. All four children went, too, the three girls determined 'not to get stuck in the kitchen because you could see it had destroyed and damaged something essential in our mother,' Byatt explains.

She knew she wanted to write 'on hearing my first fairy story'. The household was full of books, everyone recited poetry and their father would sing the Messiah gustily whenever the dishwasher was on. Yet now, anything communal - from love-ins to political parties - fills her with horror. When Byatt's own 11-year-old son died in an accident, she was approached by self-help groups of bereaved parents. 'I got letters saying: 'If you belonged to my group, you would find consolation.' And I wouldn't' Her voice is dry, emphatic. 'I feel for them, but from my own solitude. That is the way I cope with things.'

Perhaps her craving for solitude comes from being an oldest child lumbered with 'crawling infants'. Boarding school - where Byatt played Antonio to Judi Dench's Ariel - did not help. Cambridge, however, let Byatt be one of the boys. 'The men didn't think there was anything wrong with being clever in the way most girls did. Sex was a distraction and seemed immensely urgent, but really I knew talking to men was what was interesting. That's why I got so upset with the women's movement.'

Byatt feels strongly that 'a lot of women got pushed around by sisterhood in the seventies'. She believes doctrinaire feminism cramped ambition. 'When I started writing, the major writers were women as much as men - Murdoch, Lessing, Spark. Iris was dashing away all these large philosophical novels about the nature of Marxism and religion. It never occurred to me to think she was a woman or what sort of women's problems she dealt with.

'Then you got the women's movement and a kind of group prescription of what you ought to be writing about - for women, by women, about women. What happened was we got a generation of absolutely wonderful male novelists - Rushdie, Ishiguro, Swift, McEwan, Barnes, Amis, Kureishi - and lots of women who seemed quite content to write about what lesbians felt in their women's groups.'

It is true that women's writing often focuses on relationships and Byatt's novels revolve around ideas. Characters are not her strong point. But, she argues robustly: 'I don't do relationships and sex any worse than people who write novels entirely about relationships. But the moment I say that, someone will say, oh, she's arrogant, she's an intellectual, and the next word is cold.'

It irritates her and for a moment she looks hurt. 'In England, everyone believes if you think, then you don't feel,' she says. 'But all my novels are about joining together thinking and feeling.'

Byatt doesn't believe that women writers get a raw deal. She toes no party line. The women-only Orange Prize for Fiction is 'ghettoising rather than helpful'. If we want more women on the Booker shortlist, we should 'make sure there are enough on the judging panel'. According to her friend Carmen Callil: 'As least as many women have been asked as men, but most of the women refused to judge.'

Byatt concedes that contemporary women's writing is shaped by conflicting demands. Few of the great women writers of the past had children. But today women often slot creativity between childcare and managing the emotional health of the family. As a young mother, Byatt would rush to the library to work for the hour she had a cleaner at home. Her two worlds have constantly 'flickered into one another'. Problems with chapter 23 might get resolved while cooking, between 'one movement of the spoon and the next'.

She made a bargain with herself that she would write at least four fewer books in order to have four children. With each pregnancy, she took precautions - mental ones. 'I started putting complicated poetry books in the loo and would sit there learning poetry by heart. I was practising, the way you do exercises to get your figure back, but I was more interested in my mind than my figure. It seemed more important and it still does.'

Byatt has always been serious, even in the sixties when everyone else was hanging loose. In Babel Tower, Frederica - her thin, clever heroine - has become mother, teacher and absconding wife in a world of new freedoms and artistic happenings. The knowingness and innocence of the period annoyed Byatt. 'There were all these women dressing up in baby doll nighties and little short skirts. The doll-women weren't at all emancipated. They were playthings.

'I'd had this vision in the 1950s, which in many ways I think of as being a freer period, of being allowed to be a responsible grown-up. Instead of which you were supposed to play. And I never wanted to play.' She wanted subtlety and complication. But on offer was 'polymorphous perversity and the desirability of going back to the freedoms of a child.'

One of the best characters in Babel Tower is Leo, Frederica's small son. Byatt often writes about male children. 'I spent a lot of my life in female worlds and it did delight me to have a little boy,' she says, glancing quickly at the floor. In the short story July Ghost, a dead child haunts his home while his mother is haunted by the thought: 'He is dead... that will go on and on and on till the end of time.' It is unbearably poignant. 'It was the thought I actually had at the moment of the death of my son.'

Antonia Byatt looks weary. Promoting Babel Tower means 'I won't be able to think about anything except myself for the next two months.' And she'd much rather be sitting down with a taxing book. Or, failing that, the knights of the green table, O'Sullivan and Higgins.